1. Field of the Invention
The present invention relates to the field of amplifiers, and more particularly to class D amplifiers.
2. Prior Art
The introduction of high end Plasma and TFT-LCD TVs has spurred the need to use high efficiency power conversion processing elements in these TVs. A significant area where power processing takes place is the audio amplifier. The need for higher efficiencies is driven by the fact that the enclosures used are smaller and/or the TFT-LCD screens are sensitive to thermal gradients produced by heat generating components. Smaller, thinner enclosures also preclude the use of large and bulky heat sinks which are incompatible with automatic assembly. Thus audio amplifiers in these TVs are typically based on switching Class D amplifier architectures.
There are three main categories of devices currently being used as Class D amplifiers. These are:
1. Conventional modulation single supply full bridge (H-bridge). In this class of devices, the PWM signals have to be filtered before application to the speaker load. The duty cycle at each leg of the H-bridge at zero output voltage is roughly 50%. This results in non-used re-circulating currents in the filter elements, resulting in power loss even though no power is transmitted to the load.
2. Modified modulation single supply full bridge (H-bridge). This class of devices are H-bridge connected. However, unlike in the conventional method, their modulation technique allows the duty cycle to go to “zero” for no signal input. This avoids the re-circulating current at “zero” input signal. This type of Class D devices are also called “Filterless” as a result of the above described property.
3. Conventional Modulation dual supply half bridge. There are several devices that use this method. The modulation method is similar to that of the conventional H-bridge. The output filter re-circulates current with zero input signal.
Presented later herein is a table illustrating various characteristics of the above modulation techniques for comparison with the same characteristics of the present invention.